Fold fling gesture into onDragEnd

That way the fling engages in the same direction as the scroll. For example, if
you have a horizontal scroll nested inside a vertical scroll, the fling will
take place in the same direction as the scroll.

packages/flutter/lib/gestures/fling.dart

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-import 'dart:sky' as sky;
-
-import 'package:sky/gestures/arena.dart';
-import 'package:sky/gestures/recognizer.dart';
-import 'package:sky/gestures/constants.dart';
-
-// Fling velocities are logical pixels per second.
-typedef void GestureFlingCallback(sky.Offset velocity);
-
-int _eventTime(sky.PointerEvent event) => (event.timeStamp * 1000.0).toInt(); // microseconds
-
-bool _isFlingGesture(sky.GestureVelocity velocity) {
-  double velocitySquared = velocity.x * velocity.x + velocity.y * velocity.y;
-  return velocity.isValid &&
-    velocitySquared > kMinFlingVelocity * kMinFlingVelocity &&
-    velocitySquared < kMaxFlingVelocity * kMaxFlingVelocity;
-}
-
-class FlingGestureRecognizer extends GestureRecognizer {
-  FlingGestureRecognizer({ PointerRouter router, this.onFling })
-    : super(router: router);
-
-  GestureFlingCallback onFling;
-  sky.VelocityTracker _velocityTracker = new sky.VelocityTracker();
-  int _primaryPointer;
-
-  void addPointer(sky.PointerEvent event) {
-    startTrackingPointer(event.pointer);
-    if (_primaryPointer == null)
-      _primaryPointer = event.pointer;
-  }
-
-  void handleEvent(sky.PointerEvent event) {
-    if (event.pointer == _primaryPointer) {
-      if (event.type == 'pointermove') {
-        _velocityTracker.addPosition(_eventTime(event), _primaryPointer, event.x, event.y);
-      } else if (event.type == 'pointerup') {
-        sky.GestureVelocity velocity = _velocityTracker.getVelocity(_primaryPointer);
-        if (_isFlingGesture(velocity)) {
-          resolve(GestureDisposition.accepted);
-          if (onFling != null)
-            onFling(new sky.Offset(velocity.x, velocity.y));
-        }
-      }
-    }
-    stopTrackingIfPointerNoLongerDown(event);
-  }
-
-  void didStopTrackingLastPointer() {
-    _primaryPointer = null;
-    _velocityTracker.reset();
-  }
-
-  void dispose() {
-    super.dispose();
-    _velocityTracker.reset();
-    _primaryPointer = null;
-  }
-}

packages/flutter/lib/gestures/recognizer.dart

@@ -25,7 +25,7 @@ abstract class GestureRecognizer extends GestureArenaMember {
   void handleEvent(sky.PointerEvent event);
   void acceptGesture(int pointer) { }
   void rejectGesture(int pointer) { }
-  void didStopTrackingLastPointer();
+  void didStopTrackingLastPointer(int pointer);
 
   void resolve(GestureDisposition disposition) {
     List<GestureArenaEntry> localEntries = new List.from(_entries);
@@ -53,7 +53,7 @@ abstract class GestureRecognizer extends GestureArenaMember {
     _router.removeRoute(pointer, handleEvent);
     _trackedPointers.remove(pointer);
     if (_trackedPointers.isEmpty)
-      didStopTrackingLastPointer();
+      didStopTrackingLastPointer(pointer);
   }
 
   void stopTrackingIfPointerNoLongerDown(sky.PointerEvent event) {
@@ -124,7 +124,7 @@ abstract class PrimaryPointerGestureRecognizer extends GestureRecognizer {
     }
   }
 
-  void didStopTrackingLastPointer() {
+  void didStopTrackingLastPointer(int pointer) {
     _stopTimer();
     state = GestureRecognizerState.ready;
   }

packages/flutter/lib/gestures/scroll.dart

@@ -16,14 +16,26 @@ enum DragState {
 
 typedef void GestureDragStartCallback();
 typedef void GestureDragUpdateCallback(double scrollDelta);
-typedef void GestureDragEndCallback();
+typedef void GestureDragEndCallback(sky.Offset velocity);
 
 typedef void GesturePanStartCallback();
 typedef void GesturePanUpdateCallback(sky.Offset scrollDelta);
-typedef void GesturePanEndCallback();
+typedef void GesturePanEndCallback(sky.Offset velocity);
 
 typedef void _GesturePolymorphicUpdateCallback<T>(T scrollDelta);
 
+// Fling velocities are logical pixels per second.
+typedef void GestureFlingCallback(sky.Offset velocity);
+
+int _eventTime(sky.PointerEvent event) => (event.timeStamp * 1000.0).toInt(); // microseconds
+
+bool _isFlingGesture(sky.GestureVelocity velocity) {
+  double velocitySquared = velocity.x * velocity.x + velocity.y * velocity.y;
+  return velocity.isValid &&
+    velocitySquared > kMinFlingVelocity * kMinFlingVelocity &&
+    velocitySquared < kMaxFlingVelocity * kMaxFlingVelocity;
+}
+
 abstract class _DragGestureRecognizer<T extends dynamic> extends GestureRecognizer {
   _DragGestureRecognizer({ PointerRouter router, this.onStart, this.onUpdate, this.onEnd })
     : super(router: router);
@@ -39,6 +51,8 @@ abstract class _DragGestureRecognizer<T extends dynamic> extends GestureRecogniz
   T _getDragDelta(sky.PointerEvent event);
   bool get _hasSufficientPendingDragDeltaToAccept;
 
+  final sky.VelocityTracker _velocityTracker = new sky.VelocityTracker();
+
   void addPointer(sky.PointerEvent event) {
     startTrackingPointer(event.pointer);
     if (_state == DragState.ready) {
@@ -50,6 +64,7 @@ abstract class _DragGestureRecognizer<T extends dynamic> extends GestureRecogniz
   void handleEvent(sky.PointerEvent event) {
     assert(_state != DragState.ready);
     if (event.type == 'pointermove') {
+      _velocityTracker.addPosition(_eventTime(event), event.pointer, event.x, event.y);
       T delta = _getDragDelta(event);
       if (_state == DragState.accepted) {
         if (onUpdate != null)
@@ -75,7 +90,7 @@ abstract class _DragGestureRecognizer<T extends dynamic> extends GestureRecogniz
     }
   }
 
-  void didStopTrackingLastPointer() {
+  void didStopTrackingLastPointer(int pointer) {
     if (_state == DragState.possible) {
       resolve(GestureDisposition.rejected);
       _state = DragState.ready;
@@ -83,8 +98,20 @@ abstract class _DragGestureRecognizer<T extends dynamic> extends GestureRecogniz
     }
     bool wasAccepted = (_state == DragState.accepted);
     _state = DragState.ready;
-    if (wasAccepted && onEnd != null)
-      onEnd();
+    if (wasAccepted && onEnd != null) {
+      sky.GestureVelocity gestureVelocity = _velocityTracker.getVelocity(pointer);
+      sky.Offset velocity = sky.Offset.zero;
+      if (_isFlingGesture(gestureVelocity))
+        velocity = new sky.Offset(gestureVelocity.x, gestureVelocity.y);
+      resolve(GestureDisposition.accepted);
+      onEnd(velocity);
+    }
+    _velocityTracker.reset();
+  }
+
+  void dispose() {
+    _velocityTracker.reset();
+    super.dispose();
   }
 }
 

packages/flutter/lib/src/widgets/dismissable.dart

@@ -155,7 +155,7 @@ class Dismissable extends StatefulComponent {
       _fadePerformance.progress = _dragExtent.abs() / (_size.width * _kDismissCardThreshold);
   }
 
-  _handleDragEnd() {
+  void _handleDragEnd(Offset velocity) {
     if (!_isActive || _fadePerformance.isAnimating)
       return;
     _dragUnderway = false;

packages/flutter/lib/src/widgets/gesture_detector.dart

@@ -4,7 +4,6 @@
 
 import 'dart:sky' as sky;
 
-import 'package:sky/gestures/fling.dart';
 import 'package:sky/gestures/long_press.dart';
 import 'package:sky/gestures/recognizer.dart';
 import 'package:sky/gestures/scroll.dart';
@@ -28,8 +27,7 @@ class GestureDetector extends StatefulComponent {
     this.onHorizontalDragEnd,
     this.onPanStart,
     this.onPanUpdate,
-    this.onPanEnd,
-    this.onFling
+    this.onPanEnd
   }) : super(key: key);
 
   Widget child;
@@ -49,8 +47,6 @@ class GestureDetector extends StatefulComponent {
   GesturePanUpdateCallback onPanUpdate;
   GesturePanEndCallback onPanEnd;
 
-  GestureFlingCallback onFling;
-
   void syncConstructorArguments(GestureDetector source) {
     child = source.child;
     onTap = source.onTap;
@@ -65,7 +61,6 @@ class GestureDetector extends StatefulComponent {
     onPanStart = source.onPanStart;
     onPanUpdate = source.onPanUpdate;
     onPanEnd = source.onPanEnd;
-    onFling = source.onFling;
     _syncGestureListeners();
   }
 
@@ -113,13 +108,6 @@ class GestureDetector extends StatefulComponent {
     return _pan;
   }
 
-  FlingGestureRecognizer _fling;
-  FlingGestureRecognizer _ensureFling() {
-    if (_fling == null)
-      _fling = new FlingGestureRecognizer(router: _router);
-    return _fling;
-  }
-
   void didMount() {
     super.didMount();
     _syncGestureListeners();
@@ -133,7 +121,6 @@ class GestureDetector extends StatefulComponent {
     _verticalDrag = _ensureDisposed(_verticalDrag);
     _horizontalDrag = _ensureDisposed(_horizontalDrag);
     _pan = _ensureDisposed(_pan);
-    _fling = _ensureDisposed(_fling);
   }
 
   void _syncGestureListeners() {
@@ -143,7 +130,6 @@ class GestureDetector extends StatefulComponent {
     _syncVerticalDrag();
     _syncHorizontalDrag();
     _syncPan();
-    _syncFling();
   }
 
   void _syncTap() {
@@ -200,13 +186,6 @@ class GestureDetector extends StatefulComponent {
     }
   }
 
-  void _syncFling() {
-    if (onFling == null)
-      _fling = _ensureDisposed(_fling);
-    else
-      _ensureFling().onFling = onFling;
-  }
-
   GestureRecognizer _ensureDisposed(GestureRecognizer recognizer) {
     recognizer?.dispose();
     return null;
@@ -225,8 +204,6 @@ class GestureDetector extends StatefulComponent {
       _horizontalDrag.addPointer(event);
     if (_pan != null)
       _pan.addPointer(event);
-    if (_fling != null)
-      _fling.addPointer(event);
     return EventDisposition.processed;
   }
 

packages/flutter/lib/src/widgets/scrollable.dart

@@ -89,7 +89,7 @@ abstract class Scrollable extends StatefulComponent {
   GestureDragEndCallback _getDragEndHandler(ScrollDirection direction) {
     if (scrollDirection != direction || !scrollBehavior.isScrollable)
       return null;
-    return _maybeSettleScrollOffset;
+    return _handleDragEnd;
   }
 
   Widget build() {
@@ -98,11 +98,9 @@ abstract class Scrollable extends StatefulComponent {
       onVerticalDragEnd: _getDragEndHandler(ScrollDirection.vertical),
       onHorizontalDragUpdate: _getDragUpdateHandler(ScrollDirection.horizontal),
       onHorizontalDragEnd: _getDragEndHandler(ScrollDirection.horizontal),
-      onFling: scrollBehavior.isScrollable ? _handleFling : null,
       child: new Listener(
         child: buildContent(),
         onPointerDown: _handlePointerDown,
-        onGestureFlingCancel: _handleFlingCancel,
         onWheel: _handleWheel
       )
     );
@@ -183,19 +181,12 @@ abstract class Scrollable extends StatefulComponent {
     return EventDisposition.processed;
   }
 
-  void _handleFling(Offset velocity) {
+  void _handleDragEnd(Offset velocity) {
+    if (velocity != Offset.zero) {
       _startToEndAnimation(velocity: _scrollVelocity(velocity));
-  }
-
-  void _maybeSettleScrollOffset() {
-    if (!_toEndAnimation.isAnimating &&
-        (_toOffsetAnimation == null || !_toOffsetAnimation.isAnimating))
+    } else if (!_toEndAnimation.isAnimating && (_toOffsetAnimation == null || !_toOffsetAnimation.isAnimating)) {
       settleScrollOffset();
     }
-
-  EventDisposition _handleFlingCancel(sky.GestureEvent event) {
-    _maybeSettleScrollOffset();
-    return EventDisposition.processed;
   }
 
   EventDisposition _handleWheel(sky.WheelEvent event) {
@@ -570,7 +561,7 @@ class PageableList<T> extends ScrollableList<T> {
       .clamp(scrollBehavior.minScrollOffset, scrollBehavior.maxScrollOffset);
   }
 
-  void _handleFling(sky.Offset velocity) {
+  void _handleDragEnd(sky.Offset velocity) {
     double scrollVelocity = _scrollVelocity(velocity);
     double newScrollOffset = _snapScrollOffset(scrollOffset + scrollVelocity.sign * itemExtent)
       .clamp(_snapScrollOffset(scrollOffset - itemExtent / 2.0),

packages/unit/test/gestures/scroll_test.dart

@@ -25,7 +25,7 @@ void main() {
     };
 
     bool didEndPan = false;
-    pan.onEnd = () {
+    pan.onEnd = (sky.Offset velocity) {
       didEndPan = true;
     };
 

packages/unit/test/widget/gesture_detector_test.dart

@@ -21,7 +21,7 @@ void main() {
         onVerticalDragUpdate: (double scrollDelta) {
           updatedDragDelta = scrollDelta;
         },
-        onVerticalDragEnd: () {
+        onVerticalDragEnd: (Offset velocity) {
           didEndDrag = true;
         },
         child: new Container()
@@ -69,9 +69,9 @@ void main() {
     Widget builder() {
       return new GestureDetector(
         onVerticalDragUpdate: (double delta) { dragDistance += delta; },
-        onVerticalDragEnd: () { gestureCount += 1; },
+        onVerticalDragEnd: (Offset velocity) { gestureCount += 1; },
         onHorizontalDragUpdate: (_) { fail("gesture should not match"); },
-        onHorizontalDragEnd: () { fail("gesture should not match"); },
+        onHorizontalDragEnd: (Offset velocity) { fail("gesture should not match"); },
         child: new Container()
       );
     }